This invention relates in general to vehicle safety devices and in particular to a new and useful windup mechanism for a safety belt which is engaged on an automatic belt winding assembly.
Windup mechanisms serve the purpose of taking up a slack of a safety belt at an impact of the vehicle, by winding up the belt and thus minimizing the free hurl forward until the belt becomes effective.
A take-up mechanism for winding up belt has to meet three requirements. It must be capable of compensating for an existing slack (such as of 20 cm), it must be small enough to be accommodated in the available space in the vehicle, and its design must permit subsequent mounting without, or with only a minimum adaptation, on existing automatic belt winding devices which are series-manufactured and thus adequately inexpensive.
German OS No. 22 62 889 discloses a winding device wherein the belt reel is formed by a rotary piston which is actuated by drive gases from a pyrotechnical charge. In this device, however, the rotary piston equipped with a vane can be rotated through only about 310.degree. which is not sufficient for doing away from a larger slack of the belt.
Another belt winding device of the above kind with a windup mechanism equipped with a rotary piston-type of a motor is known from German AS No. 25 10 514. This rotary piston motor comprises two annular chambers which are bounded by a shaft, a cylindrical wall, and a front and a rear cover and separated from each other by an annular disc extending between the shaft and the cylindrical wall, and two vanes, one in each of the annular chambers, extending over the entire circumferential cross-sectional area of the respective chamber, with one vane in each of the annular chambers being firmly connected to the shaft and to the annular disc (first vane, second vane), and, in the front chamber, a third vane being firmly connected to the front cover, and in the rear chamber, a fourth vane being connected to the rear cover, and this cover being connected to the cylindrical wall. The gases produced by the drive charge pass through bores in the shaft into the two annular chambers, with, in the front chamber, the first vane, and in the rear chamber, the fourth vane being exposed to the gases and rotatable, independently of each other and along with the parts connected thereto, until the first vane butts against the third vane, and the fourth vane butts against the second vane.
It is true that a rotation of the belt reel through about 600.degree. is thereby made possible, i.e. even a substantial slack can be removed, however, a relatively complicated rotary piston motor is required.
Further, in the same device according to German AS No. 25 10 514, the belt reel is mounted for rotation on a journal secured to the rotary piston motor and on a journal supported on the housing of the automatic belt winding mechanism. To form a positive clutch, the side disc facing the rotary piston motor belt reel is designed as a notched wheel cooperating with a pawl mechanism for blocking the automatic belt winding assembly, with the periphery of the side disc being provided with a plurality of bores into which bolts are engageable by the action of the drive gases of the charge, to couple the drive pulley of the motor to the belt reel. This augments the axial length of this device, relative to a conventional automatic belt winding unit, substantially only by the width of the rotary piston motor, however, due to the many differences over the existing automatic belt winding units manufactured in large series, a subsequent mounting of the pull-off mechanism thereon is not possible.